1. Field of Invention
The present invention relates to a wafer-bump structure and, more particularly, to a wafer-bump structure made in a process including the steps of zincating and electroless nickel/immersion gold (“ENIG”) instead of the step of under-bump metallization (“UBM”) and including the step of forming a pillar bump by printing conductive metal paste instead of electroplating gold, thus improving soldering thereof to other devices and reducing the cost thereof.
2. Related Prior Art
Referring to FIG. 2, there is shown a conventional wafer-bump structure 5 made in a conventional under-bump metallization process. The wafer-bump structure 5 includes a semiconductor die 50, an under-bump metal layer 60 and a pillar bump 70. The semiconductor die 50 is formed with a surface 501. At least one die pad 51 is embedded in the semiconductor die 50. A passivation layer 52 is formed on the surface 501 of the semiconductor die 50 and a surface of the die pad 51. The passivation layer 52 includes at least one aperture for allowing access to a portion of the surface of the die pad 51.
In the making of the conventional wafer-bump structure 5, the under-bump metallization process is executed to provide the die pad 51. The cost of the conventional under-bump metallization process is high while the yield of the conventional under-bump metallization process is low. Moreover, in the making of the conventional wafer-bump structure 5, a gold-electroplating process is used to form the pillar bump 70. The gold-electroplating process is however expensive, and the resultant pillar bump 70 is expensive for being made of gold entirely. This problem is getting worse since the price of gold is skyrocketing.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.